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VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old December 12th, 2017, 07:55   #16
Mike_04GolfTDI
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So if I understand correctly, the problem is basically that the car is hard to start when cold?

If it's not the glowplugs, then the next thing I would check is the electric fuel pump in the tank. Those commonly fail, and the car will still run, but might take a few extra seconds to start. That's what happened when mine failed.

Every time you turn the key on, that pump should run for a couple seconds. It's accessible through a hatch under the right-rear seat. It should be easy to hear it turn on, especially if you open that hatch (just three screws...easy).

Or you can disconnect the fuel line that comes out of the middle of the fuel filter and put the end in a bottle to collect the fuel. When you turn the key on (don't crank the engine) there should be a healthy stream of fuel spraying out of that line. If not, the pump is dead.

Here's a video of a guy looking at this pump: https://www.youtube.com/watch?v=7VcDiE4Mew0
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Last edited by Mike_04GolfTDI; December 12th, 2017 at 08:05. Reason: Added video link
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Old December 12th, 2017, 08:00   #17
BobnOH
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Quote:
Originally Posted by Rhynri View Post
The carfax isn't particularly clear about this. The people who sold it to me actually knew to check it, and said it looked to be in good shape, but we know visual inspections aren't a kosher method for checking timing belts.
It's my intent to do the timing belt/water pump changeout, but I wanted to inspect the camshaft first, so that way I can do the whole shebang at once if it needs it. Q: would an older belt be contributing to the smokey starts? (say, relaxed timing or something). I swear I've read something to that effect.
Carfax provides a variety of info, sometimes useful, sometimes not.
The belt is not making smoke (unless it jumped time, unlikely). Are the glow plugs working?
Could be injector seals. I recommend lots of reading for the fueling system, it's different.
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Old December 12th, 2017, 08:07   #18
Rhynri
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That seems like a good lead. I have great ears and I've never heard it run.

To clarify: Starts when it's been sitting (say, overnight) are smokey year around and right now (10.9F) it pretty much takes multiple 10 second cranks before it'll start and stay running, and clouds of that white-blue diesel smoke.

Basically, it starts like an old diesel tractor.

Edit: But it runs very well once it actually starts and subsequent starts, even cold, within a few hours pop right off with minor smoke. It also starts better when it's been parked with the nose elevated.

Last edited by Rhynri; December 12th, 2017 at 08:10. Reason: Clarification
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Old December 12th, 2017, 08:58   #19
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If it turns out that the electric fuel pump isn't working, make sure you check the fuse before you replace it. You might get lucky and it's just a fuse. I can't remember which one it is.

Also, replace it soon if you need to, because it's bad for the tandem pump to run in a state where it's sucking fuel. It's a positive displacement rotary vane style pump and if it's pulling through a restriction that may cause cavitation and damage the pump.

The tandem pump is located on the end of the cylinder head, on the driver's side. One part of it is a vacuum pump and the other pumps fuel. If you follow the fuel lines from your fuel filter, across the front of the engine, one of them will lead to the inlet of the tandem pump. That pump is the reason your car may still run without the electric pump (although possibly poorly).
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Old December 12th, 2017, 10:03   #20
JB05
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A quick check for the in-tank pump is to pull the thermostatic T on the fuel filter and see if the filter is full or not. It should be full
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Old December 12th, 2017, 13:05   #21
B3achbum
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Default Check glowplugs are they NGK?

So the BEW motor historically had reports of hard starting in the cold, and VW had a series of TSB campaigns to address customer complaints. The fixes were often at no charge to the customers, but had mixed results.

Mine was recommended for go tsb at the dealer, and was done - but incompletely.
I think it would have been in 2008.
I had hard starting in the cold for a couple of years as a Result of the TSB work, UNTIL I found this thread:

http://forums.tdiclub.com/showthread.php?t=328868

It is very detailed with great pictures that still come through (no photobucket problem ). You might want to run you VIN through vincoder:
https://www.vindecoderz.com/EN/Volkswagen
, or call a VW dealer to find out which if any glow plug TSB's have been performed on your car.

My car now starts in cold within .25 seconds, almost instantaneously.
(But haven't tried in the MN winters!!!)

Last edited by B3achbum; December 12th, 2017 at 18:58. Reason: Fixed typo/grammar
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Old December 12th, 2017, 14:12   #22
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Quote:
Originally Posted by Rhynri View Post
I can do the whole shebang at once if it needs it.
Q: would an older belt be contributing to the smokey starts? (say, relaxed timing or something). I swear I've read something to that effect.
Just wanted to make sure you were aware of the belt.

I would think the belt would have to be so loose the injection timing is retarded to cause white smoke and maybe problems starting.
Don't run the car if it's that bad.
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Old December 12th, 2017, 19:07   #23
Rhynri
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Originally Posted by wonneber View Post
Just wanted to make sure you were aware of the belt.
Thanks!

Quote:
Originally Posted by wonneber View Post
I would think the belt would have to be so loose the injection timing is retarded to cause white smoke and maybe problems starting.
Don't run the car if it's that bad.
Ever write something then look at it later and be like "I'm an idiot". Yeah, if it had somehow slipped it'd be really loose, and you know, that VCDS run I just did would have shown it. Derp. :P

Last edited by Rhynri; December 12th, 2017 at 19:08. Reason: Fixed broken quote
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Old December 15th, 2017, 09:17   #24
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Originally Posted by Mike_04GolfTDI View Post
Also, replace it soon if you need to, because it's bad for the tandem pump to run in a state where it's sucking fuel. It's a positive displacement rotary vane style pump and if it's pulling through a restriction that may cause cavitation and damage the pump.\
So, I'm pretty sure the electric one isn't running. But I had a random question about this:

Wouldn't the tandem pump not be pulling against a restriction because of the return line loop back to the fuel filter? To me it looks like you have the loop from the tank to the filter, then that tank-side return, and the loop from the filter to the engine and a filter side return. Or am I misunderstanding this and it's actually sending all the way back to the tank from the engine?

Not doubting you, just trying to increase my understanding of how this all works!
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Old December 15th, 2017, 11:33   #25
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Quote:
Originally Posted by Rhynri View Post
So, I'm pretty sure the electric one isn't running. But I had a random question about this:
Wouldn't the tandem pump not be pulling against a restriction because of the return line loop back to the fuel filter? To me it looks like you have the loop from the tank to the filter, then that tank-side return, and the loop from the filter to the engine and a filter side return. Or am I misunderstanding this and it's actually sending all the way back to the tank from the engine?
Not doubting you, just trying to increase my understanding of how this all works!
The electric pump in the tank sends fuel to the inlet connection of the fuel filter under the hood.

The connection that comes out the middle of the canister is the clean fuel that goes to the tandem pump.

The other connection that has a plastic "T" fitting is the return line. This is needed because the tandem pump pumps a larger volume of fuel than what the engine consumes. There are passages in the head that provide fuel to the injectors, and there's a mechanism to keep those passages at a certain pressure. excess fuel is returned through the return line (otherwise the pressure would just go up and up until something broke, probably the pump).

The plastic "T" fitting in the top of the fuel filter is basically a temperature controlled diverter valve. When fuel is cold, it dumps the fuel back into the filter, which is supposed to help warm it up so the fuel doesn't gel. When the fuel is warm, it just goes back to the tank.

Underneath the car there is a fuel cooler. I believe it would be on the return line. In a PD engine, the fuel can get really hot, so that fuel cooler can be used to cool it down.

If the tandem pump has to pull fuel through the filter, and the possible restriction caused by a dead electric pump, then there may be cavitation occurring at the inlet, and maybe a lack of adequate fuel supply to the injectors.

A dead electric pump in your tank could definitely cause poor starting issues such as you've experienced.

Interesting reading: https://www.michael-smith-engineers....y-PD-Pumps.pdf
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Old December 15th, 2017, 12:59   #26
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Originally Posted by Mike_04GolfTDI View Post
The electric pump in the tank sends fuel to the inlet connection of the fuel filter under the hood...

...Interesting reading: https://www.michael-smith-engineers....y-PD-Pumps.pdf
Fascinating! Thanks for the great explanation. This thread has been very educational.
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Old December 15th, 2017, 13:24   #27
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Out of curiosity I looked up some properties of diesel fuel, and it takes 15" Hg (inches of mercury) or -7.346565 PSI to cause air that is entrained in the fuel to vaporize causing bubbles.

Could the tandem pump pull a vacuum of -7 PSI or 15"Hg when the electric pump doesn't work? I would say very likely yes. That's not much of a stretch for a positive displacement pump powered by a 1.9L turbo diesel engine, pulling fuel through a long thin hose, a dead electric pump, and a fuel filter.

So the electric pump provides just a little pressure to reduce or eliminate the possibility of air or vapor entrained in the fuel from forming bubbles.

If you go ahead and replace that electric pump, I'd be curious to hear if it solves your problem. Hopefully it does!
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Last edited by Mike_04GolfTDI; December 15th, 2017 at 13:27.
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Old December 15th, 2017, 14:01   #28
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What does your intake manifold look like? I have an ALH and a bew, had to clean out the manifold twice with smoking as you describe..Pop the pipe and get a flashlight or take some flash pics, could be plugged.
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Old January 7th, 2018, 11:07   #29
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Originally Posted by Mike_04GolfTDI View Post
Out of curiosity I looked up some properties of diesel fuel, and it takes 15" Hg (inches of mercury) or -7.346565 PSI to cause air that is entrained in the fuel to vaporize causing bubbles.

Could the tandem pump pull a vacuum of -7 PSI or 15"Hg when the electric pump doesn't work? I would say very likely yes. That's not much of a stretch for a positive displacement pump powered by a 1.9L turbo diesel engine, pulling fuel through a long thin hose, a dead electric pump, and a fuel filter.

So the electric pump provides just a little pressure to reduce or eliminate the possibility of air or vapor entrained in the fuel from forming bubbles.

If you go ahead and replace that electric pump, I'd be curious to hear if it solves your problem. Hopefully it does!
That science is freaking fascinating! I love that stuff.

On the the latest progress report.

I replaced the electric pump, and it was most definitely dead. It didn't solve the hard starting problem, but it did improve on it in a crucial way - once it catches it runs much smoother and stays running. And either way I'm reducing the load on my tandem pump, so worth doing. I've also replaced both rear calipers because they were hanging up when you let the e-brake off, and only one was working. In addition, I did the driver side CV and bled clutch and all four corners (as you'd expect.) That's part of why it took me so long to get back to this thread, so my apologies.

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Originally Posted by indysoto View Post
What does your intake manifold look like? I have an ALH and a bew, had to clean out the manifold twice with smoking as you describe..Pop the pipe and get a flashlight or take some flash pics, could be plugged.
It might be clogged a little, but if this was influencing the starting, I'd expect it to start hard on a second start attempt. I could start it (with a hard start), back it out of the garage, shut it off. It'd start immediately as long as I tried again within a short interval (or longer if it's been running longer). So it's probably some of the heat retained in the heads easing the start. But that's just a guess. Which leads me to:

The glow plug TSB. I walked into the local VW, and they pulled the service/TSB records for me, and it hasn't had the glow plug/hard start TSB done to it. Which is good in a way, because that means it's a likely cause. The bad news is that they no longer perform this service for you free of charge.

How do I go about doing this myself? Replace plugs with the 7v NGKs, modify harness as linked above, get a tune with the GP mod applied to it? If there are more steps than that, please chime in. And could someone clarify the proper part number for those plugs? I'd hate to put the wrong thing in.

As always, thanks in advance for all the wonderful input.

Last edited by Rhynri; January 7th, 2018 at 11:40. Reason: Added post number for indysoto quote
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